Cell-to-cell communication is required for many biological processes such as differentiation, proliferation, and homeostasis. One system utilized by a wide range of eukaryotes is the Notch-signaling pathway. This pathway, especially the Notch receptor, is also critical for functional tumor angiogenesis. Thus, inhibition of Notch receptor function, blockage of the Notch receptor, and/or blockage of the Notch-signaling pathway are potential strategies for anti-cancer compositions and therapies. Small molecule inhibitors of the Notch receptor have proven to be toxic because they suppress wild type (normal) tissue expression of Notch receptors throughout the body. Thus, different members of the Notch-signaling pathway should be considered as potential targets for therapeutics.
A vasculature ligand for the Notch receptor is Delta 4 or Delta-like 4 (DLL-4). Largely expressed in the vasculature, DLL-4 is critical for vascular development (Yan et al., Clin. Cancer Res., 13(24): 7243-7246 (2007); Shutter et al., Genes Dev., 14(11): 1313-1318 (2000); Gale et al., Proc. Natl. Acad. Sci. USA, 101(45): 15949-15954 (2004); Krebs et al., Genes Dev., 14(11): 1343-1352 (2000)). Mice heterozygous for DLL-4 are embryonically lethal due to major defects in vascular development (Gale et al., Proc. Natl. Acad. Sci. USA, 101(45): 15949-15954 (2004); Duarte et al., Genes Dev., 18(20): 2474-2478 (2004); Krebs et al., Genes Dev., 18(20): 2469-2473 (2004)). The expression of DLL-4 can be induced by VEGF (Liu et al., Mol. Cell. Biol., 23(1): 14-25 (2003); Lobov et al., Proc. Natl. Acad. Sci. USA, 104(9): 3219-3224 (2007)). In sum, DLL-4 can negatively regulate VEGF signaling, in part through repressing VEGFR2 and inducing VEGFR1 (Harrington et al., Microvasc. Res., 75(2): 144-154 (2008); Suchting et al., Proc. Natl. Acad. Sci. USA, 104(9): 3225-3230 (2007)). Exquisite coordination between DLL4 and VEGF is essential for functional angiogenesis.
In addition to its physiological role, DLL-4 is up-regulated in tumor blood vessels (Gale et al., Proc. Natl. Acad. Sci. USA, 101(45): 15949-15954 (2004); Mailhos et al., Differentiation, 69(2-3): 135-144 (2001); Patel et al., Cancer Res., 65(19): 8690-8697 (2005); Patel et al., Clin. Cancer Res., 12(16): 4836-4844 (2006); Noguera-Troise et al., Nature, 444(7122): 1032-1037 (2006)). Blockade of DLL-4 potently inhibited primary tumor growth in multiple models (Noguera-Troise et al., Nature, 444(7122): 1032-1037 (2006); Ridgway et al., Nature, 444(7122): 1083-1087 (2006); Scehnet et al., Blood, 109(11): 4753-4760 (2007)). The inhibition of DLL-4 was even effective against tumors that are resistant to anti-VEGF therapy. The combinatorial inhibition of both DLL-4 and VEGF provided an enhanced anti-tumor activity. Interestingly, unlike VEGF inhibition that reduces tumor vessel formation, DLL-4 blockade leads to an increase in tumor vasculature density wherein the vessels are abnormal, cannot support efficient blood transport, and are effectively nonfunctional. Thus, DLL4 provides a potential target for cancer treatment.
Interactions between Notch receptors and their ligands represent an evolutionarily conserved pathway important not only for cell fate decisions but also in regulating lineage decisions in hematopoiesis and in the developing thymus (Artavanis-Tsakonas et al. 1999, Science 284:770-776; Skokos et al. 2007; J. Exp. Med. 204:1525-1531; and Amsen et al. 2004, Cell 117:515-526). It has been recently shown that DLL-4-Notch1 inhibition leads to a complete block in T cell development accompanied by ectopic appearance of B cells and an expansion of dendritic cells (DC) that can arise from Pro-T cell to DC fate conversion within the thymus (Hozumi et al. 2008, J. Exp. Med. 205(11):2507-2513; Koch et al. 2008, J. Exp. Med. 205(11):2515-2523; and Feyerabend et al. 2009, Immunity 30:1-13). Thus, there is accumulating evidence that Notch signaling is critical for the determination of cell fate decision from hematopoietic progenitor cells. Furthermore, a feedback control of regulatory T cell (Treg) homeostasis by DCs in vivo has been shown (Darrasse-Jeze et al. 2009, J. Exp. Med. 206(9):1853-1862). However, the role of Notch signaling in controlling the origin and the development of DCs and consequently Treg homeostasis is still unknown. This is a question that is clinically important because identifying new methods of inducing Treg expansion could be used as a treatment for autoimmunity diseases and disorders.
Other DLL antagonists and their uses are disclosed in WO 2007/143689, WO 2007/070671, WO 2008/076379, WO 2008/042236, and WO/2008/019144. Therefore, there is a need in the art for therapeutic agents capable of targeting the DLL-4-Notch pathway and thereby inhibiting, or even preventing, tumor angiogenesis and growth.